ScudCloud is a non official open-source desktop client app for Slack.

ScudCloud improves the Slack integration with desktop featuring:

   * multiple teams support
   * native system notifications
   * count of unread direct mentions at launcher/sytray icon
   * alert/wobbling on new messages
   * optional tray notifications and "Close to Tray"
   * follow your desktop activity and will stay online while you're
     logged in (if correct packages are installed)

WWW: https://github.com/raelgc/scudcloud